16 March, 2008 at 10:19 am (rpg theory) (, , , , )

Given that choice is and important part of roleplaying, how do people make choices? There are useful theories out there (including game theory, with which I have a passing familiarity). I’ll try building another one so that it hopefully has something useful to say about roleplaying.

This model is specifically about how people make choices in the context of roleplay and that affect the rp. Extending the model is not particularly hard and is left as an exercise for the reader. The limitation is essentially arbitrary.

I also try out sketching a model for immersion as it is seen through this piece of theory. The threefold model is another example.

Some definitions

Filter is a criterion that assigns a weight to different options people have regarding their play. In case someone in the audience is mathematically inclined, a given filter is a mapping from the decision space (this is the emulation space [emspace] for those familiar with Kuma’s AGE model) to real line; generally speaking, the entire real line is not needed and one can work with a given interval or other subset.

Example filters: What would my character do? Will this result in total party kill? What will this say about me as a person? Is this appropriate to the genre?
Example filters for the more elaborate model: How much will everyone enjoy this? How genre-appropriate is this?

A filter is strong when it makes sharp contrasts between different options; likewise, a weak filter makes little difference. These are not exact definitions and should generally be used as a part of comparative phrases (they imply comparison to some unstated standard if not used in such a way).

A simple model

Every participant has a number of filters. Each filter accepts certain options and rejects others. In math: Filter is an indicator function of a subset of the decision space. It assigns value 1 to any option that is within the subset and 0 to any that is not.

When making a decision, participant applies filters, one at a time, with each application further restricting the possible choices (or at least not adding any). When the remaining options are sufficiently close to each other, the participant makes that choice. “Sufficiently” depends on how important the occasion is, how tired the person is, level of attention, and so forth.

The order filters are applied in is a matter of playing style and other influences.

Assumptions of this simple model

This is not a good model. It makes the following assumption (and others): That people always either reject or accept a given option; essentially, this model assume two-valued logic. This is not very accurate.

A more elaborate model

Filters work as above, expect that they can get values up to an arbitrary positive value on the real line (this can, but need not, be fixed). That is: A given filter assignes some value to all potential options the player has at a decision point (in nontrivial cases the assigned values differ from one option to the next). For desirable (according to that criterion) options, the value is high. For undesirable ones it is low. These are multiplied over all the used filters until one is sufficiently larger than the others. The option with highest value is then implemented and a choice is made.


Character immersion happens when player identifies with a character to great degree. Filter theory sees immersion as a process where the player has one or few very strong filters, so that it seems the player is not making choices at all. Typically this filter is “What does (would) my character do?”. This is clearly distinct from the disruptive behaviour sometimes known as “my guy-syndrome”, in which the relevant players uses the character’s actions as excuses for bad behaviour. In this model, players who disrupt the game and use the character as an excuse don’t make heavy use of the “what would my character do”-filter, but some other, more harmful, one.

The threefold model is a theory about filters. G, D and S all signify emphasis on given (family of) filters: dramatist GM has a strong “does this make a good story”-filter, for example. This is very explicitly not true of GNS: It is not about the way decisions are made, but rather what decisions are thought to be important, which certainly is prone to influencing the strength and priorisation of the filters that are used.

It will do little harm to think about the filters you use and of those that other people you game with use, and the order in which they are likely to be applied. Something might even be learned by such actions.

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